As a process for producing an alkyl nitrite by reaction of an alkyl alcohol with nitrogen monoxide and oxygen, Japanese Unexamined Patent Publication No. 11-189,570 and No. 6-298,706 disclose a process in which an alkyl alcohol is fed into a top portion of a reaction column and allowed to fall from the top portion to the bottom portion through a middle portion of the reaction column; separately, nitrogen monoxide and oxygen gasses are fed separately or together into the bottom portion of the reaction column and allowed to flow upward through the reaction column and react with the falling alkyl alcohol to produce an alkyl nitrite; and the resultant gas fraction containing the alkyl nitrite is collected through an outlet located in the top portion of the reaction column.
This process is however, unsatisfactory in that nitric acid is produced as a by-product, in a relatively large amount, and thus a large amount of the nitrogen materials for the process is in advantageously consumed. Therefore, it is desirable that the nitric acid is effectively utilized to increase the efficiency of the production of the target alkyl nitrite.
Japanese Unexamined Patent Publication No. 6-25,104 discloses a process, for continuously producing dimethyl carbonate from carbon monoxide and methyl nitrite, in which nitrogen monoxide produced as a by-product is utilized to react with oxygen and methyl alcohol to regenerate methyl nitrite and in this methyl nitrite-regeneration procedure, nitric acid is utilized as a nitrogen-supply source. In this process, nitric acid is thermally decomposed to generate nitrogen oxides. However, the decomposition is carried out with an unsatisfactory efficiency and the effective decomposition temperature is very limited. In this reaction system, nitric acid and nitrogen monoxide may contact methyl alcohol. However, the inventors of the present invention found that in the reaction system for producing methyl nitrite from nitrogen monoxide, oxygen and methyl alcohol, oxygen gas fed into the reaction system causes the concentrations of oxygen and nitrogen dioxide in the reaction gas to increase, and therefore, the production of methyl nitrite from nitric acid, nitrogen monoxide and methyl alcohol with a high efficiency is very difficult.
Also, Japanese Unexamined Patent Publication No. 11-189,570 discloses a process for producing an alkyl nitrite by withdrawing a liquid fraction collected in a bottom portion of an alkyl nitrite regeneration reaction column and containing nitric acid from the reaction column, and cooling and recycling the withdrawn liquid fraction through the reaction column and a cooler. In connection with this reaction system, the inventors of the present invention found that while a contact of nitric acid and the alkyl alcohol with nitrogen monoxide occurs in the reaction system, the reaction system contains oxygen and nitrogen dioxide in increased concentrations due to the feed of oxygen into the reaction system and, therefore, the production of the alkyl nitrite from nitric acid, nitrogen monoxide and the alkyl alcohol with a high production efficiency is very difficult.
Chemistry Letters, 1029 (1976) discloses that when nitrogen dioxide is produced by a reaction of nitric acid with nitrogen monoxide as shown in reaction formula (1):NO+2HNO3→3NO2+H2O  (1)in an initial stage of the reaction (1), a reaction shown in reaction formula (2) occurs.NO+HNO3→NO2+HNO2  (2)
However, the reaction (2) is disadvantageous in that the equilibrium of the reaction (2) greatly deviates to the original system side, and thus, the production of nitrogen dioxide and nitrous acid in high concentration is difficult and, when the equilibrium of the reaction (2) is moved to the resultant product system side, as the solubility of nitrogen dioxide in water is relatively high and, in the reaction system, nitrogen dioxide, nitrous acid and nitric acid are equilibrates with each other, an increase in the concentration of nitrogen dioxide or in the reaction pressure, causes the production of nitric acid to increase and as a result, the production of nitrogen dioxide at a high concentration becomes difficult. Due to the above-mentioned disadvantages, the inventors of the present invention concluded that the above-mentioned process is unsatisfactory as an industrial practice for producing nitrogen dioxide and nitrous acid from nitric acid. Further, Encyclopaedia Chinrica, volume 1, 32nd Printing in Reduced Size, page 665, discloses a process for producing nitrogen monoxide by reducing a concentrated nitric acid with a bismuth, copper, led or mercury metal or iron oxide (II) or diarsenic trioxide. This process utilizes a stoichiometric reaction and thus, the reducing material comprising the above mentioned metal or oxide must be employed in a large amount. Therefore, the above-mentioned process is inadequate in industrial practice.